Hydraulic powder press



Oct. 15, 1957 H. R. GREGORY ETA!- HYDRAULIC POWDER PRESS Filed June 27, 1955 hired States atent Patented Oct. 15, 1957 HYDRAULI PGJVDER PRESS Harry Rex Gregory and Maurice Kendal, Cheltenham,

England, assignors to Coal Industry (Patents) Limited, London, England, a British company This invention relates to improvements in presses and one object of the invention is to provide a press for the manufacture of briquettes without a binder from materials in divided form, e. g. fine coal or metallic or nonmetallic powders, according to the method described in our prior patent application Nos. 32,592/53 and 4,257/54.

in the method described in our said prior application a mass of particles while under pressure is caused to undergo angular shear strain of such magnitude and distribution as to produce a briquette of high strength.

The said prior patent application also describes a method of making a briquette wherein pressure is applied to a quantity of particles to form a compacted mass and thereafter while the mass is held under pressure, the whole mass or an external face thereof is caused to undergo a substantial change in shape or configuration to set up within the mass angular shear strain having such magnitude and distribtuion as to produce a briquette of high strength. Such change in shape or configuration may be general and take place over the whole mass or over the whole of one or more external faces, e. g. by distorting the cross section of the mass from a rectangle to a parallelogram or from a circle to an ellipse, or the change may be local, as for example by forming a recess or depression at some locality in an external face.

While the press of the present invention is envisaged as being of particular application to the manufacture of riquettes by the method described in the above mentioned prior patent application (which may be seen for fuller details) it is to be understood that the invention is not limited to this application but may also be applied to the manufacture of any other article which can be made by means of a press.

According to the present invention there is provided a press having a main ram for applying the working load during the working stroke, a multiple plunger tool having two or more relatively movable plungers for transmitting the load to the material to be treated, and a pressure fluid operated control system operative to control the relative movement of said plungers during the working stroke of the main ram.

The invention in another aspect consists in a press having a main ram for applying the working load during the working stroke, a multiple plunger tool having two or more relatively movable plungers for transmitting the load to the material to be treated, and a control system operated by fluid pressure derived from the reaction of the said material against the load applied by the main ram for controlling relative movement of the said plungers during the working stroke of the said ram.

The working load may be applied to the main ram by a mechanical or hydraulic system, and this system may be independent of and separate from the hydraulic system for controlling the relative movement of the plungers.

The invention in yet another aspect consists in a press having a main ram for applying the working load during the Working stroke, a multiple plunger tool having two or more relatively movable plungers for transmitting the load to the material to be treated, and a control system operated by fluid pressure derived from the reaction of the said material against the load applied by the main ram and arranged to maintain the said plungers against relative motion until the said fluid pressure reaches a predetermined level.

In one form of the invention the tool has two relatively movable plungers for transmitting the load to the material to be treated and the control system is arranged to maintain the said two plungers against relative motion until the said fluid pressure reaches a predetermined level, thereby enabling the whole or the greater part of the working load of the main ram to be applied to one only of the plungers after the said predetermined level of pressure is reached.

Preferably the control system is provided with a pressure sensitive device so constructed and arranged that when the said determined level of pressure is reached the device enables the pressure to fall to a value which is relatively low compared to the said predetermined level. The tool may have two plungers which are held together under the action of the pressure of the fluid, the said pressure falling to a relatively low value after a pre-determined maximum pressure has been reached whereby the whole or the greater part of the working load is then applied to the piston.

The two plungers may be in the form of two co-axial plungers of which one is in the form of an annulus and the other in the form of a piston working within the said annulus and the pressure operating the said control systerm may be obtained from the pressure of fiuid in a chamber arranged within the plunger assembly.

Other features of the invention will appear from the followin description given by way of example only with reference to the accompanying drawings in which:

Figure l is a diagram of an arrangement of a press according to the invention,

Figure 2 a sectional elevation of a relief valve, and

Figure 3 a diagram of a second arrangement of a press according to the invention.

Figure 1 illustrates a press arrangement comprising a mould it for retaining a mass of particles fed into it from a hopper ii, and a multiple plunger tool 12 attached to a main ram 18 for operating on said particles. The tool 12 has two relatively movable plungers 12a, 12b, an inner plunger 12b being in the form of a piston slidably and co-axially mounted within an annular plunger 12a. The latter is integral with cylinder 12c providing a chamber for fiuid and the plunger 12b is integral with a piston 12d which is itself secured to a main ram 18 by a pillar 19. A hydraulic circuit is coupled to a port 12a of the cylinder 12C, hydraulic fluid e. g. oil, being fed from a reservoir 13 by a pump 14 through a relief valve 15 and a nonreturn valve 16. A relief valve 17 provides a return path for the fluid to the reservoir 13 from the cylinder 12c.

In operation a requisite quantity of particles of the material to be treated is fed from hopper 11 into mould Zltl, whereupon the tool 12 acting as a unitary assembly, i. e. with plungers 12a and 12b held together due to the hydraulic pressure, is caused to enter mould Ill by the action of mechanical or hydraulic means (not shown) operating to exert a working load F on the main ram 18. During this part of the Working stroke the entire area of the upper surface of the particles in mould 10 is subjected to compressive force, the Working load F being distributed between the two plungers 12a and 12b. held in a retracted position relative to plunger 122. (as shown in Figure l) the eifect of this operation is to form a compacted mass of particles of approximately cylindrical form but having a relatively short upstanding central plug on its upper surface.

As the compressed particles present increasing relf plunger 12b is.

sistance to the tool the pressure of the fluid in chamber 12c correspondingly increases until at a predetermined value depending on the setting of relief valve 17, the fluid in chamber12c escapes through valve 17 to reservoir 13. The plungers 12a. and 12b are thus no longer held together and the whole (or at least the greater part) of the working load F is applied via plunger 12b (which is driven forward relatively to plunger 12a.) to the central plug formed in the preceding operation so that the material in this plug is forced into the remainder of the compacted mass to form finally a briquette of substantially cylindrical form.

On releasing the pressure on the tool 12 the fluid pressure in cylinder 12c falls, valve 17 and relief valve 15 close, and pump 14 is able to supply fluid to the cylinder 12c recharging the ram for the next operation.

In Figure 2 is illustrated a relief valve for use in the system of Figure 3 and which valve is the subject of our British patent application No. 17,389/ 55. This relief valve comprises a hollow body 20 in which is a cylinder 21 to which fluid can be admitted through an inlet connection 22 and from which fluid can escape through an onlet connection 23. A piston 24 is slidably arranged in the cylinder 21 and is loaded by a compression spring 25 which is located, and of which the pressure can be adjusted, by means of a screw-threaded sleeve 26 and a nut 27 with a lock nut 28. Attached to the piston 24 is a valve ball 29 which can be held by the piston 24 against a seat 30 to close the inlet connection 22. A vent hole 31 permits escape of any fluid which may leak past the piston 24. I

The relief valve of Figure 2 functions as follows:

When the valve ball 29 is on the seat 30 and there is no fluid pressure in the cylinder 21 the whole force of the spring 25 tends to keep the ball on its seat so that a high fluid pressure in the inlet connection 22 is necessary to unseat the valve ball. As soon as the valve ball is unseated the fluid pressure acts on the end surface of the piston 24 and therefore acts against the spring 25 so that the pressure in the cylinder 21 must fall to a low value relatively to that necessary to open the valve before the spring can return the ball to its seat. When the valve ball is held ofi its seat the valve oflers only a low resistance to flow.

Figure 3 illustrates an arrangement comprising the mould 10, hopper 11, multiplunger tool 12 and ram 18 of Figure 1. From a reservoir 13 a pump 14 supplies hydraulic fluid under pressure through a relief valve 15 and a non-return valve 16 and a pipe 41 to the ram 12, any excess fluid passing from the valve 15 through a pipe 40 back to the reservoir 13. A pipe 42 connects to the ram cylinder 120 a relief valve 43 which is constructed as shown in Figure 2. A pipe 44 is connected to the'outlet of the relief valve 43 and leads to a low pressure relief valve 45. A pipe 46 branching from the pipe 44 leads to a needle valve 47 through which fluid can pass to a pipe 48 to the reservoir 13.

The arrangement shown in Figure 3 functions as follows. During the working stroke the fluid pressure in the cylinder 12c is required to raise to a relatively high value (for example 3,000 lbs. per square inch) with little or no relative movement between the plungers 12a. and 121 However, as soon as this pressure is reached a rapid fall to a much lower value (for example 300 lbs. per square inch) is required, the bulk of the fluid being discharged from cylinder 12c at this lower pressure. When the ram 19 is being raised the cylinder 12 is full of fluid; when the ram 18 is forced down, the pressure of the fluid in cylinder 12 increases and this pressure is transmitted through pipe 42 to valve 43;

when the pressure is suflicient to open valve 43, fluid passes through pipe 44 and valve but the latter maintains the pressure within valve 43 at a value high enough to ensure that valve 43 does not close. At the end of the working stroke ram 18 is raised, whereupon the pressure in cylinder 12c drops very rapidly and the pressure in valve 43 also drops so that this valve can close, whereupon valve 45 closes and the system is ready for the next cycle. The needle valve 47 permits a slow leak which dissipates any back pressure which may arise in the piping connecting valves 43 and 45 in the interval between successive operations. The needle valve 47 also enables the system to operate correctly even if there is a small leak through the valve 43 when the latter is. closed; the setting of needle valve 47 is not critical. The construction and arrangement of valve 43 enables the transition from high pressure to low pressure in the cylinder 12:: to take place very rapidly.

The lower end of plunger 12'! may be of approximately 7 conical form as shown in Figure l or it may be domed or flat. The lower edge of plunger 122. may be flat, as shown, as it may be of frusto-conical form widening downwardly outwards.

It will also be understood that modifications may also he made in the relative posit-ions of plungers 12a and 12b and the mode of application of the pressure. Thus for example the lower end of plunger 12b may project beyond the lower end of plunger 12a. during the first part of the working stroke so as to form a recess in the material to be treated with a surrounding annular projection, and during the remainder of the working stroke the Whole or the greater part of the working load may be transferred to the annular plunger 128. so as to operate on the annular projection previously formed.

We claim:

1. A press-comprising a main ram applying the working force, a solid inner plunger rigidly secured to said main ram, an annular outer plunger surrounding said inner plunger, a fluid-containing cylinder secured to said outer plunger and surrounding an end of said nected to said cylinder and responsive to fluid pressure within said cylinder, said fluid-control means allowing the fluid pressure in said cylinder to build up to relatively high value during the working stroke, and

then causing it to fall to a relatively low value.

2. A press as claimed in claim 1, said fluid control means comprising a relief valve comprising a body in which is a chamber with an inlet and an outlet, a valve element in said chamber, a spring resiliently loading said valve element to close said inlet to said chamber, and a valve piston fitting in said chamber and secured to said valve element, the cross-sectional area of said chamber being many times larger than that of said inlet.

. 3. A press as claimed in claim 2, said fluid-control means comprising a second relief valve operatively connected to said outlet and maintaining the fluid pressure in said chamber at a level such that said spring'cannot overcome the fluid pressure on said valve piston to move said valve element to close said inlet after said valve element has been moved against the action of said spring by.

fluid pressure in said inlet.

927,283 France Apr. 28, 1947 

